This invention relates to improved cobalt-base alloys containing hafnium and a high proportion of chromium which are particularly suitable for high-temperature molten glass environments.
In one of its more specific aspects, the invention relates to articles manufactured from the alloys, particularly articles made by casting.
In certain industrial applications there is a need for alloys which possess high rupture strength and high oxidation resistance at high temperatures. Among such applications are those involved, for example, in the glass fiber industry, where filaments are produced by passing a molten mineral material, for example, glass, through the foraminous walls of a chamber adapted for rotation at high speeds, the chamber being known as a spinner, the filaments being emitted through fiberizing orifices of the wall due to the centrifugal action to which the molten material is subjected upon rotation of the spinner. Such spinners are typically operated when spinning glass fibers at temperatures of about 2050.degree. F. and rotation speeds of about 2050 RPM. It is advantageous, from a production cost standpoint, for the rotation speed to be as high as possible to increase the rate at which filaments are emitted through the fiberizing orifices. However, higher spinner rotational speeds result in a reduction in spinner life due to the limited strength and corrosion resistance of the prior art alloys used in spinners. Also, cost savings are realized by fiberizing lower cost batch formulations such as higher viscosity wool glass, but prior art alloys have not had the necessary mechanical strength to fiberize at the higher temperatures required for higher viscosity wool glass. The stress rupture properties of prior art alloys fall off rapidly above 2100.degree. F.
The best materials known, prior to the present invention, for use in such applications are those defined and claimed in U.S. Pat. No. 3,933,484 issued Jan. 20, 1976 and U.S. Pat. No. 4,497,771 issued Feb. 5, 1985, the alloy composition of U.S. Pat. No. 4,497,771 being substantially the same as that of U.S. Pat. No. 3,933,484 except that the alloy composition of U.S. Pat. No. 4,497,771 has a lower tantalum content.
The alloy compositions of the present invention have substantially improved strength and corrosion resistance compared with the alloy compositions disclosed in U.S. Pat. Nos. 3,933,484 and 4,497,771.